This invention relates to a computer network system in which a plurality of computers are connected through a network and data are packet-transferred between the computers, to a network file server in the computer network system and to a data transfer controlling method thereof.
Drastic progresses have been made in recent years in the improvement of a high speed operation of CPUs (Central Processing Units), a large capacity of magnetic disks and reduction of their cost of production, and a high speed operation of networks, and constitution of client-server systems for connecting one or more computers through a network and operating them cooperatively have been vigorously attempted. In such client-server systems, the data is stored in the server and the client can gain access to the data stored in the server by making access to the server. The systems of this kind provide the advantage that a plurality of clients can share the data of the server.
On the other hand, large quantities of images and sounds can now be handled easily by a computer in the field of multimedia communication due to the progress of digitization technologies of the images and the sounds and due also to the progress of compression technologies as described, for example, in "Media Processing: A New Design Target", IEEE MICRO, August, 1996, pp. 6-9. For this reason, a digital studio system which handles the images and the sounds as digital information by personal computers (PCs) or workstations (WSs) and edits and casts the digital information has become wide spread, as described in "Nikkei Multimedia", August, 1995, p. 86, for example.
The digital studio system is the system which conducts efficient image edition by the PC or the WS using a random accessible magnetic disk in place of image edition using tapes according to the prior art. At present, however, such a PC or a WS has been constituted into a stand-alone system, that is, a system that does not share data with other digital studio apparatuses. Nonetheless, the form of the client-server system is more preferred to the stand-alone system in view of the fact that the edition work of the images is not carried out by only one editor and the edition result is shared preferably by a greater number of parties as possible. Because the digital studio system uses a standard file access interface such as a file access function defined by "The C Programming Language Second Edition", 1988, p. 169-174 or "Win 32 System Services: The Heart of Windows 95 & Windows NT", 1996, p. 24, for example, a network file system (NFS) must be used in order to convert the digital studio system to the client-server system. An example of the network file system is the NFS. This NFS is described in Hal Stern "NFS & NIS", published by K. K. Askie, 1992, p. 184.
The network file system comprises clients, a server and a network for connecting them, and the server includes a main storage device, a secondary storage device, and so forth.
When a file access request is generated from the client to the server in the network file system according to the prior art, the server prepares a buffer for the secondary storage device in the main storage device, reads out the data corresponding to the access request from the secondary storage device and stores the data in the buffer for the secondary storage device. Next, to transfer the data stored in the buffer for the secondary storage device to the client through the network, a header comprising a data transfer length, a target machine ID such as an ID of the requesting client, etc., is added to the data in the form of a packet and then this packet is transferred to the client through the network. In this instance, in order to shape the packet form, a buffer for the packet is prepared on the main storage device separately from the buffer for the secondary storage device, and the header information is first described into the buffer for the packet comprising a continuous physical address space inside the main storage device. Next, the data in the buffer for the secondary storage device is copied to the remaining areas in the buffer for the packet. In consequence, in the buffer for the packet, the header and the data are arranged in the continuous physical space inside the main storage device and can be transferred as the packet data to the network.